The present invention relates to a dry etching method for fabricating a microdevice such as for example a micro-semiconductor device or a micromagnetic device, to a microfabrication process or method using this dry etching method and to a dry etching mask.
When manufacturing a microdevice, such as a micro-semiconductor device and a micromagnetic device, a microfabrication process utilizing both a lithography technology and an etching technology is executed abundantly.
The lithography technology is used to fabricate an etching mask by forming a micro-pattern on a photosensitive film such as a resist film coated on a surface of a work layer, and the etching technology is used to transfer thus formed micro-pattern of the etching mask to the work layer.
As one of the etching technology for providing a microstructure, there is a reactive ion etching method utilizing plasma of a low pressure reaction gas. If a plasma of a reaction gas CF4 or CCl4 is provided in the reactive etching of a magnetic material with transition metal elements such as Fe, Co or Ni for example as the main ingredient, a halogen compound can be formed as well as done in the reactive etching of a semiconductor material. However, since the halogen compound of the transition metal has an extremely higher coupling energy than that of a halogen compound of a semiconductor element, it is not only hard to evaporate but also is unaffected by the sputtering reaction. Therefore, an etching reaction of the transition metal halogen compound seldom progresses.
In order to solve these problems, a new reaction system using a plasma of a carbon monoxide gas had been developed and, by improving this system, a dry etching method using as a reaction gas a carbon monoxide gas with an additive of nitrogen consisting compound gas was proposed (Japanese patent publication 08253881A and Isao Nakatani, xe2x80x9cFabrications of Microstructures of Magnetic Materialsxe2x80x9d, Jpn. J. Appl. Mag., Vol.22, No. 11, pp.1383-1389, 1998).
In these literatures, described are experimental results of a reactive ion etching on a permalloy thin-film using as a reaction gas a carbon monoxide (CO) gas with an additive of an ammonia (NE3) gas in order to make a pattern with a size of about 0.6 xcexcm, and of the similar reactive ion etchings on a silicon (100) monocrystal and on an aluminoborosilicate glass for comparison. The results are that a ratio of an etching rate of the silicon (100) monocrystal with respect to an etching rate of the permalloy is four, and that a ratio of an etching rate of the aluminoborosilicate glass with respect to an etching rate of the permalloy is nine.
However, in the latest etching process requesting a more fine etching pattern, if a ratio of etching rates between the mask and the work layer is so small as this level, it is difficult to transfer the fine pattern of the mask on the work layer with maintaining its precise shape. This is because the mask itself will be etched and will be deformed before the desired part of the work layer is entirely etched, and also because etching of the work layer will progress from mask edge due to side etching. Particularly, this tendency is strong in a pattern with a trench width or a line width of 0.1 xcexcm or less and thus it is very difficult to transfer such the fine pattern on a work layer with keeping its precise shape.
It is therefore an object of the present invention to provide a dry etching method, a microfabrication method and a dry etching mask, whereby a microfabrication with keeping its precise shape can be performed.
According to the present invention, a dry etching method include a step of preparing a layer to be etched and a step of dry-etching the layer using a mask made of a tantalum or a tantalum nitride under a reaction gas of a carbon monoxide with an additive of a nitrogen containing compound gas.
According to the present invention, also, a microfabrication method includes a step of forming a mask made of a tantalum or a tantalum nitride on a layer to be etched, and a step of dry-etching the layer using the mask under a reaction gas of a carbon monoxide with an additive of a nitrogen containing compound gas.
In dry-etching process executed under a reaction gas of a carbon monoxide with an additive of a nitrogen containing compound gas, a tantalum or a tantalum nitride with a low etching rate is used as a mask material. Thus, it is possible to increase a ratio between the etching rate of the mask and that of the layer to be etched, and therefore the mask itself will not be deformed by etching and also etching of the layer to be etched will not progress from mask edge due to side etching. As a result, a fine micro-pattern can be transferred on the work layer with keeping its precise shape.
It is preferred that the step of forming a mask includes forming a resist pattern on the layer to be etched and then sputtering a mask layer using a tantalum target or a tantalum nitride target.
It is also preferred that the step of forming a mask includes forming a resist pattern on the layer to be etched and then reactive-sputtering a mask layer using a tantalum target under a reaction gas containing at least a nitrogen gas. In this case, the reaction gas containing at least a nitrogen gas may be a mixture gas of an argon gas and a nitrogen gas.
According to the present invention, furthermore, a dry etching mask used in dry-etching under a reaction gas of a carbon monoxide with an additive of a nitrogen containing compound gas is made of a tantalum or a tantalum nitride.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.